Feat(UI): Exit PiP when destroying UI
Feat(UI): Exit PiP when destroying UI

The UI can open up Picture-in-Picture mode, through the PiP button,
but it does not automatically leave PiP mode when being destroyed.
This CL adds leaving PiP mode to the destroy process.

Closes #3553

Change-Id: I6830a7ceed7e4ca4fbd0e7d36b8257d564e0226c

tvoli/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,tvoli/shaka-player,tvoli/shaka-player,shaka-project/shaka-player